A vehicle may contain automatic safety restraint actuators that are activated responsive to a vehicle crash for purposes of mitigating occupant injury. Examples of such restraint actuators include air bags, seat belt pretensioners, and deployable knee bolsters.
One objective of an automatic safety restraint system is to mitigate occupant injury, thereby not causing more injury with the automatic restraint system than would be caused by the crash had the automatic restraint system not been activated. Notwithstanding the protective benefit of these automatic safety restraint actuators, there is generally both a risk and a cost associated with the deployment thereof. Generally, it is desirable to only activate automatic safety restraint actuators when needed to mitigate injury because of the expense of replacing the associated components of the safety restraint system, and because of the potential for such activations to harm occupants. This is particularly true of air bag restraint systems, wherein occupants too close to the air bag at the time of deployment--i.e. out-of-position occupants--are vulnerable to injury or death from the deploying air bag even when the associated vehicle crash is relatively mild. Moreover, occupants who are of small stature or with weak constitution, such as children, small adults or people with frail bones are particularly vulnerable to injury induced by the air bag inflator. Furthermore, infants properly secured in a normally positioned rear facing infant seat (RFIS) in proximity to a front seat passenger-side air bag are also vulnerable to injury or death from the deploying air bag because of the close proximity of the infant seat's rear surface to the air bag inflator module.
Air bag inflators are designed with a given restraint capacity, as for example, the capacity to protect an unbelted normally seated fiftieth percentile occupant when subjected to a 30 MPH barrier equivalent crash, which results in associated energy and power levels which can be injurious to out-of-position occupants. While relatively infrequent, cases of injury or death caused by air bag inflators in crashes for which the occupants would have otherwise survived relatively unharmed have provided the impetus to reduce or eliminate the potential for air bag inflators to injure the occupants which they are intended to protect.
One technique for mitigating injury to occupants by the air bag inflator is to reduce the power and energy levels of the associated air bag inflator, for example by reducing the amount of gas generant in the air bag inflator, or the inflation rate thereof. This reduces the risk of harm to occupants by the air bag inflator while simultaneously reducing the restraint capacity of the air bag inflator, which places occupants a greater risk for injury when exposed to higher severity crashes.
Another technique for mitigating injury to occupants by the air bag inflator is to control the rate of inflation rate or the capacity of the inflator responsive to a measure of the severity of the crash. However, the risk of injury to such occupants would not be mitigated under the conditions of higher crash severity when the inflator is intentionally made aggressive in order to provide sufficient restraint for normally positioned occupants.
Yet another technique for mitigating injury to occupants by the air bag inflator is to control the activation of the air bag inflator responsive to the presence, position, and size of the occupant, or to the severity of the crash. For example, the air bag inflator can be disabled if the occupant weight is below a given threshold. Moreover, the inflation capacity can be adjusted by controlling the number of inflation stages of a multi-stage inflator that are activated. Furthermore, the inflation power can be adjusted by controlling the time delay between the firings of respective stages of a multi-stage inflator.
One measure of restraint capacity of an air bag inflator is the amount of occupant kinetic energy that can be absorbed by the associated air bag system, whereby when the occupant collides with the gas filled air bag, the kinetic energy of the occupant is converted to potential energy via the pressurization of the air bag, and this potential energy is dissipated by venting pressurized gases from the air bag. As a vehicle in a crash is decelerated, the velocity of an unrestrained occupant relative to the vehicle increases. Preferably, the occupant restraint process is commenced early in the crash event so as to limit the amount of occupant kinetic energy that must be absorbed and thereby minimize the associated restraint forces and accelerations of and loads within the occupant. If the occupant were a simple inertial mass without friction relative to the vehicle, the kinetic energy of the occupant would be given by 1/2 M.multidot.V.sup.2, where M is the mass of the occupant and V is the occupant velocity relative to the vehicle. If a real occupant were represented by an interconnected set of bodies, some of which have friction relative to the vehicle, each body of which may have differing velocities relative the vehicle, the above equation would apply to the motion of the center of gravity of the occupant. Regardless of the representation, occupants of larger mass will have a larger kinetic energy for the same velocity relative to the vehicle. Therefore, an occupant weight sensor is useful in an air bag system with variable restraint capacity to enable the restraint capacity to be preferentially adapted to the weight, or mass, of the occupant.
Except for some cases of oblique or side-impact crashes, it is generally desirable to not activate an automatic safety restraint actuator if an associated occupant is not present because of the otherwise unnecessary costs and inconveniences associated with the replacement of a deployed air bag inflation system. Occupant presence can be detected by a seat weight sensor adapted to provide either a continuous measure of occupant weight or to provide a binary indication if the occupant weight is either above or below a specified weight threshold.
Known methods for detecting the position of a seated vehicle occupant have been developed that incorporate detection systems having infrared beams, ultra-sound beams, capacitive sensors, CCD camera sensors and passive infrared detectors.
Known ultrasound beams use conventional methods of sending out an acoustic pulse and measuring the time delay before the reflected pulse returns. In order to obtain a three dimensional profile of an occupant's position using the known beam based methods, a system would require many individual beams each having a corresponding dedicated receiver.
With respect to the other noted arrangements, passive type systems do not work well in extremely warm environments. Capacitive sensor type systems are only proximity sensors with no ability to give profile information. CCD systems require complex image analysis software and optical hardware to produce three dimensional information, and thus are potentially cost prohibitive.
Sound waves are typically generated directly from the motion of a vibrating surface such as a speaker cone. Sound waves may also be generated in mid air by mixing two separate sound waves each of a distinct frequency and of sufficient amplitude so that the non-linearity of the air generates two additional sets of sound waves, one having a frequency given by the difference in the frequencies of the original waves, the other having a frequency given by the sum of the frequencies of the original waves, whereby the generated wave at the difference frequency has greater energy than the generated wave at the sum frequency. Mr. Elwood Norris of American Technology Corporation has developed what is referred to as a "HyperSonic Sound" system (HSS.TM.) which incorporates this principle by mixing two ultrasonic waves which differ in frequency by an amount which corresponds to an audio signal so as to generate high fidelity sound in mid air as an improvement to the conventional loudspeaker. For example, a 200 KHz wave and a 210 KHz wave simultaneously generating by a common ultrasonic transducer generate an audible 10 KHz sonic wavefront along the ultrasonic beam emitted by the ultrasonic transducer. This HyperSonic.TM. Sound is explained further in a white paper of the same title available from the American Technology Corporation World Wide Web site at http://www.atcsd.com/HTML/whitepaper.html. The HSS.TM. is used as a replacement for an audio speaker system, and generates the difference wave from separate ultrasonic beams generated by a common ultrasonic transducer. However, the literature on HSS.TM. does not teach the use of separate ultrasonic transducers for purposes of detecting objects or the profile thereof.